Investigation of the aircraft wreckage and components found no indication of any mechanical malfunction that may have initiated or contributed to the accident sequence. Weather was also not considered to be a factor. Although the initiating event in the accident sequence could not be determined, it is most likely that the pilot was filling the water bucket near the edge of the lake and drifted toward the shoreline, where the left skid tubes contacted the trees. This then resulted in the loss of control of the aircraft, ending up in a dynamic rollover condition. The damage patterns are consistent with erratic blade movement that resulted in main rotor strikes of the tail boom and torsion shearing of the main rotor mast. Given the pilot's interaction with the medic and the presence of a Reactine bottle at the accident site, it is probable that the pilot took some of the medication. It is also probable that allergy symptoms and/or antihistamine effects distracted the pilot from the surrounding obstacles and the complexity of the task. Although there are differing opinions regarding the effects of Reactine, most of the studies found some central nervous system effects from its use. Those effects could have affected the pilot's ability to stay alert and be aware of all surrounding mission factors. It is up to pilots to evaluate if they are in a safe medical condition to exercise the privileges of their licence. The extended amount of time taken to set up the water bucket before the occurrence flight could have been caused by a lack of familiarity and/or experience with the equipment. The unusual use of the longline for an operation that did not require it also indicated unfamiliarity with this type of operation. The pilot also had difficulties carrying out the first water pickup just before the accident. Combined, these events indicate that the pilot was likely operating beyond his comfort level. Previous experience and training did not provide sufficient skills and awareness to conduct water bucketing in a very active forest-fire environment.Analysis Investigation of the aircraft wreckage and components found no indication of any mechanical malfunction that may have initiated or contributed to the accident sequence. Weather was also not considered to be a factor. Although the initiating event in the accident sequence could not be determined, it is most likely that the pilot was filling the water bucket near the edge of the lake and drifted toward the shoreline, where the left skid tubes contacted the trees. This then resulted in the loss of control of the aircraft, ending up in a dynamic rollover condition. The damage patterns are consistent with erratic blade movement that resulted in main rotor strikes of the tail boom and torsion shearing of the main rotor mast. Given the pilot's interaction with the medic and the presence of a Reactine bottle at the accident site, it is probable that the pilot took some of the medication. It is also probable that allergy symptoms and/or antihistamine effects distracted the pilot from the surrounding obstacles and the complexity of the task. Although there are differing opinions regarding the effects of Reactine, most of the studies found some central nervous system effects from its use. Those effects could have affected the pilot's ability to stay alert and be aware of all surrounding mission factors. It is up to pilots to evaluate if they are in a safe medical condition to exercise the privileges of their licence. The extended amount of time taken to set up the water bucket before the occurrence flight could have been caused by a lack of familiarity and/or experience with the equipment. The unusual use of the longline for an operation that did not require it also indicated unfamiliarity with this type of operation. The pilot also had difficulties carrying out the first water pickup just before the accident. Combined, these events indicate that the pilot was likely operating beyond his comfort level. Previous experience and training did not provide sufficient skills and awareness to conduct water bucketing in a very active forest-fire environment. The pilot undertook a water-bucketing mission for which he did not have the required training and experience. The pilot engaged in flight operations with pronounced allergy symptoms, which probably contributed to reducing his ability to perform complex multi-task missions. It is probable that the pilot took a quantity of an allergy medication that could have affected the pilot's ability to stay alert and be aware of all surrounding mission factors. The operator had no system in place to ensure that flight crews did not undertake missions or use equipment for which they were not trained.Findings as to Causes and Contributing Factors The pilot undertook a water-bucketing mission for which he did not have the required training and experience. The pilot engaged in flight operations with pronounced allergy symptoms, which probably contributed to reducing his ability to perform complex multi-task missions. It is probable that the pilot took a quantity of an allergy medication that could have affected the pilot's ability to stay alert and be aware of all surrounding mission factors. The operator had no system in place to ensure that flight crews did not undertake missions or use equipment for which they were not trained. The operator put in place several internal and external audit processes to ensure that pilot training meets all requirements on an ongoing basis. The operator developed a competency card listing all aircraft types and other operations that the individual has been trained on and authorized to perform.Safety Action Taken The operator put in place several internal and external audit processes to ensure that pilot training meets all requirements on an ongoing basis. The operator developed a competency card listing all aircraft types and other operations that the individual has been trained on and authorized to perform.